JEC COMPOSITES MAGAZINE - Issue #52 - October 2009 - 13

EQUIPMENT EQUIPMENT EQUIPMENT EQUIPMENT Focus The pitch-catch modes are used to inspect composite materials containing honeycomb structures. The transmitter sends acoustic energy into the part, which is received by the receiver. In a bonded condition, a portion of the acoustic energy is attenuated by the components of the structure. When the probe is placed over a disbonded area, the amount of energy returned to the receiver is greater, resulting in an amplitude change. Olympus Corporation is an international company operating in industrial, medical, and consumer markets, specializing in optics, electronics and precision engineering. Olympus instruments contribute to the quality of products and add to the safety of infrastructure and facilities. Olympus NDT is a world-leading manufacturer of innovative nondestructive testing instruments that are used in industrial and research applications ranging from aerospace, power generation, petrochemical, civil infrastructure, and automotive to consumer products. Leading edge testing technologies include ultrasound, ultrasound phased array, eddy current, and eddy current array. Its products include flaw detectors, thickness gages, industrial NDT systems, automated systems, industrial scanners, pulser-receivers, probes, transducers, and various accessories. Fig. 4: Bond testing pitch-catch mode. This technique was recently adapted to allow the reliable detection of a disbond (25 mm x 25 mm) located on the far side below 40 mm of honeycomb structure, like a type E defect. A new high-voltage differential probe was specifically designed for a difficult and timeconsuming inspection of an Airbus airplane. This remarkable result is now referenced in an Airbus service bulletin. sandwich panels are inspected with through-transmission methods in which a relatively high-amplitude ultrasound beam travels through the part and a receiving transducer located on the other side measures the signal attenuation. Results are typically presented as C-scan images. This technique is widely used and is very reliable. However, it is impossible to use it in a maintenance environment as the required access from both sides of the aircraft structure is impossible. fluids, and crushed cores. Low-frequency transducers and tracking of the backwall signal is necessary and must be used in a very intelligent way. Delamination of the outer skin and disbonds between outer skin and the core are characterised by a total attenuation of the backwall signal. Ultrasonic testing Ultrasound is the most widely used technique for inspecting composite structures. There are a large variety of appropriate ultrasonic instruments available. Typically, ultrasound travels very well in composite laminated structures and it can detect anomalies quite easily. Unfortunately, in sandwich structures the ultrasound is extremely attenuated due to the inhomogeneity and low density of the core structure. Therefore, the use of ultrasound for sandwich structures requires more specialized features in instruments. In a manufacturing environment, large Fig. 6: Olympus EPOCH XT. Fig. 5: Principle of the ultrasonic resonance technique. Ultrasound allows the detection of inner and outer skin disbonds, presence of A technique was recently developed to detect disbonds between the inner skin and the core. The technique uses a broad-bandwidth 1 MHz probe which creates resonance in the structure underneath the probe when it is excited by a powerful square wave pulse. The instrument’s receiver filter is tuned to the thickness of the structure and to work at the corresponding half-wavelength. Presence of a disbond will reduce the stiffness of the structure causing a No52 October 2009 / jec composites magazine

JEC COMPOSITES MAGAZINE - Issue #52 - October 2009

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #52 - October 2009